The present invention relates to angioplasty procedures, and more particularly, to a system and device for preventing arterial plaque from dislodging from the arterial wall during procedures such as, for example, percutaneous transluminal coronary angioplasty (PTCA) or percutaneous transluminal angioplasty (PTA), especially carotid PTA, and entering into the bloodstream where the embolic debris can occlude the flow of oxygenated blood to vital organs, such as the brain, which can cause devastating consequences to the patient. The present invention also relates to methods for using such a system and device.
In typical carotid PTA procedures, a guiding catheter or sheath is percutaneously introduced into the cardiovascular system of a patient through the femoral arteries and advanced through the vasculature until the distal end of the guiding catheter is in the common carotid artery. A guidewire and a dilatation catheter having a balloon on the distal end are introduced through the guiding catheter with the guidewire sliding within the dilatation catheter. The guidewire is first advanced out of the guiding catheter into the patient""s carotid vasculature and is directed across the arterial lesion. The dilatation catheter is subsequently advanced over the previously advanced guidewire until the dilatation balloon is properly positioned across the arterial lesion. Once in position across the lesion, the expandable balloon is inflated to a predetermined size with a radiopaque liquid at relatively high pressure to radially compress the atherosclerotic plaque of the lesion against the inside of the artery wall and thereby dilate the lumen of the artery. The balloon is then deflated to a small profile so that the dilatation catheter can be withdrawn from the patient""s vasculature and the blood flow resumed through the dilated artery. As should be appreciated by those skilled in the art, while the above-described procedure is typical, it is not the only method used in angioplasty.
In angioplasty procedures of the kind referenced above, abrupt reclosure may occur or restenosis of the artery may develop over time, which may require another angioplasty procedure, a surgical bypass operation, or some other method of repairing or strengthening the area. To reduce the likelihood of the occurrence of abrupt reclosure and to strengthen the area, a physician can implant an intravascular prosthesis for maintaining vascular patency, commonly known as a stent, inside the artery across the lesion. Stents are usually delivered in a compressed condition to the target location and then are deployed into an expanded condition to support the vessel and help maintain it in an open position. The stent is usually crimped tightly onto a delivery catheter and transported in its delivery diameter through the patient""s vasculature. The stent is expandable upon application of a controlled force, often through the inflation of the balloon portion of the delivery catheter, which expands the compressed stent to a larger diameter to be left in place within the artery at the target location. The stent also may be of the self-expanding type formed from, for example, shape memory metals or super-elastic nickel-titanum (NiTi) alloys, which will automatically expand from a compressed state when the stent is advanced out of the distal end of the delivery catheter into the body lumen.
The above non-surgical interventional procedures, when successful, avoid the necessity for major surgical operations. However, a danger which is always present during these procedures is the potential for particles of the atherosclerotic plaque, which can be extremely friable, breaking away from the arterial wall. For example, during deployment of a stent, the metal struts of the stent can possibly cut into the stenosis and shear off pieces of plaque which become embolic debris that will travel downstream and lodge somewhere in the patient""s vascular system. Pieces of plaque material can sometimes dislodge from the stenosis during a balloon angioplasty procedure and become released into the bloodstream. When any of the above-described procedures are performed in the carotid arteries, the release of emboli into the circulatory system can be extremely dangerous and sometimes fatal to the patient. Debris that is carried by the bloodstream to distal vessels of the brain can cause these cerebral vessels to occlude, resulting in a stroke, and in some cases, death. Therefore, although cerebral percutaneous transluminal angioplasty has been performed in the past, the number of procedures performed has been limited due to the justifiable fear of causing an embolic stroke should embolic debris enter the bloodstream and block vital downstream blood passages.
Medical devices have been developed to attempt to deal with the problem created when debris or fragments enter the circulatory system following treatment utilizing the above-identified procedures. Some techniques which have had limited success include the placement of a filter or trap downstream from the treatment site to capture embolic debris before it reaches the smaller blood vessels downstream. However, there have been problems associated with filtering systems, particularly during the expansion and collapsing of the filter within the body vessel. If the filtering device does not have a suitable mechanism for closing the filter, there is a possibility that trapped embolic debris can backflow through the open end of the filter and enter the blood-stream as the filtering system is being collapsed for removal from the patient. In such a case, the act of collapsing the filter device may actually squeeze trapped embolic material through the opening of the filter. In other instances, the rate of blood percolating through the filtering material may be slower than the normal blood flow which can either cause the filtering material to tear or cause the filter to dislodge from the deployed position due to the build up of fluid pressure behind the filter. Moreover, should the filter become clogged with debris, there is a possibility that blood circulation past the clogged filter will be insufficient for the downstream vessels. If a filter should become clogged when in use in the carotid arteries, blood flow could be diminished to the vessels leading to the brain. While the brain may be capable of functioning for a short period of time without sufficient blood flow, blood stoppage of more than thirty to forty seconds could cause the patient to experience a seizure. If the physician administering the procedure is unaware that the filtering device is clogged and that there is little or no blood flowing to the brain, the injury to the patient can be as devastating as if an emboli itself had caused blockage of the cerebral arteries.
In light of the above, it becomes apparent that there remains a need for a device or method that will prevent friable plaque from breaking away from arterial walls during intravascular procedures and forming emboli in the bloodstream, which is easy and safe to deploy, and that may be implanted for extended periods of time with minimal adverse impact or immunological response to the patient. Such a system or device would be advantageous if it prevents the need to catch and remove embolic material in the bloodstream by preventing such an occurrence in the first place. The inventions disclosed herein satisfy these and other needs.
The present invention provides a system and device for trapping embolic debris which may be created during the performance of a therapeutic interventional procedure, such as a balloon angioplasty or stenting procedure, to prevent the emboli from entering into the bloodstream and lodging and blocking blood vessels downstream from the interventional site. The present invention is particularly useful while performing an interventional procedure in critical arteries, such as the carotid arteries, in which downstream blood vessels can become blocked with embolic debris, including the main blood vessels leading to the brain or other vital organs. The present invention is particularly advantageous since any embolic debris which may be created during the interventional procedure is never actually released into the bloodstream, eliminating the need to deploy a filtering device to catch and remove debris in the bloodstream, the task performed by many prior art blood filters and embolic catching systems. Rather, the present invention employs the use of a xe2x80x9csafety netxe2x80x9d or filter which traps the plaque against the vascular wall where the stenosis is located, basically xe2x80x9cencapsulatingxe2x80x9d the area to be treated to prevent any embolic debris from entering the bloodstream in the first place. As a result, a physician will have a high degree of confidence that any embolic debris which may be created during the interventional procedure will not enter the bloodstream since this xe2x80x9csafety netxe2x80x9d creates a barrier that prevents particles from being released into the bloodstream.
A filtering or plaque-trapping device for trapping plaque against a vascular wall made in accordance with the present invention may include a tubular shaped net which is made from a blood permeable and biocompatible material having expansion members attached to each end of the tubular net. The expansion members are expandable from a contracted or collapsed position to an expanded position to contact the wall of the blood vessel to maintain the tubular netting affixed against the wall of the blood vessel where the area of plaque or stenosis is located. This plaque-trapping device xe2x80x9cencapsulatesxe2x80x9d the area of plaque with a fine meshing that filters or prevents embolic material from being released into the bloodstream.
Each expandable member can be made from a single expandable ring which can be deployed utilizing a delivery catheter made in accordance with the present invention. In another embodiment of the invention, the expandable ring can be made from a self-expanding material such as Nitinol (NiTi) alloy which allows the expandable rings to self-expand to contact the wall of the vessel and maintain the tubular netting in place over the area of plaque. Alternatively, the expandable rings could also be made from a material which can be expanded through the use of a controlled force, such as the inflation of a balloon, which allows the physician to deploy the device over the area of plaque before the interventional procedure starts. Once the plaque-trapping device is in place, the physician can treat the area of plaque utilizing balloon angioplasty techniques or stenting procedures which will compress the plaque build-up and enlarge the diameter of the blood vessel to allow greater blood flow through that region. Regardless of whether a balloon angioplasty procedure or stenting procedure is performed, the plaque-trapping device remains permanently implanted within the patient since the device is made from a blood permeable and biocompatible material. Thus, the tubular net provides a means for encapsulating the compressed area thus preventing the release of any created emboli into the bloodstream.
In one embodiment of the invention, at least one strut is attached to each end ring of the device to help maintain a set longitudinal length for the plaque trapping device and help maintain the expandable members in proper alignment. As a result, during deployment of the device, there is less chance that the tubular net would be improperly positioned in the area of treatment, resulting in the full length of the tubular net being maintained over the area of plaque build-up. Thereafter, a larger primary stent can be placed through the internal lumen of the tubular net to crush the plaque build-up and increase the diameter of the blood vessel.
Since the plaque-trapping device remains within the patient""s vasculature, it is possible to use a primary stent with the present invention which can be designed with larger xe2x80x9ccellsxe2x80x9d or wider gaps between the struts of the stent. As a result, the primary stent can be made much more flexible and will be more easily maneuverable through the patient""s vasculature allowing the stent to be designed having a lower profile to enable the physician to reach tight, distal lesions. Also, since a flexible net is placed between the primary stent and the area of plaque, there is less possibility of the struts of the stent xe2x80x9cdiggingxe2x80x9d into the plaque to shear off pieces which can cause emboli. The present device reduces the risk of acute or long term stroke in carotid procedures, reduces risk of renal failure due to the release of embolic particles into the bloodstream during renal procedures, and reduces the risk of losing a limb or a portion of the limb caused by the blockage of a vital artery in peripheral vascular procedures.
In another embodiment of the present invention, the expandable members located at the end of the tubular net portion may be stents which can either be selfexpanding or deployable by balloon inflation or other expansion means. The use of stents at the ends of the tubular net allows for secure placement of the device within the vasculature of the patient. Once the device is in place, balloon angioplasty can be performed or, alternatively, a stenting procedure can be performed to crush the plaque and maintain the blood vessel in an open position.
The present invention is also directed to a delivery catheter which provides a two-stage deployment of both the plaque trapping device and the primary stent used in the interventional procedure. The delivery catheter includes an inner member having a mounting region which allows the primary stent to be mounted thereon, along with a second mounting region utilized for mounting the plaque-trapping device. In one particular embodiment of the present invention, the mounting region for the plaque-trapping device is distal to, and has a smaller diameter than, the mounting region for the primary stent to allow greater ease in crossing highly stenosed regions of a blood vessel. As a result, the plaque-trapping device can be placed immediately into the area of treatment to provide the physician with a high level of comfort knowing that as the larger portion of the delivery catheter is being positioned through the stenosis, any inadvertent crushing of the plaque which could create embolic debris will be immediately trapped by the plaque-trapping device. Again, the plaque-trapping device and delivery catheter provides the physician with a higher level of confidence when performing high-risk interventional procedures since the plaque-trapping device provides a virtual fail-safe system and method for preventing the release of embolic debris into the bloodstream.
Other features and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments of the invention, when taken in conjunction with the accompanying exemplary drawings.